Experimental evaluations of a pilot nanofiltration system with respect to NOM and BOM removals and stable permeability with appropriate pre-treatments: a case study in Korea

A pilot-scale nanofiltration (NF) membrane system, operated at the Bansong water treatment plant of Changwon City in Korea for more than 1.5 years, was evaluated and compared with a pilot-scale granular activated carbon (GAC) and full-scale conventional treatment (CT) processes, in terms of the removal efficiencies of disinfection by-products (DBPs) formation potential and biodegradable organic matter (BOM). Nakdong river surface water (dissolved organic carbon (DOC)=2.5∼6.3 mg l⁻¹) was utilized as the water source. The membrane system was also evaluated with respect to membrane permeability (along with flux decline) and flux recovery by chemical cleaning, along with the demonstration of pre-treatment alternative (combinations of conventional processes and microfiltration (MF) membrane) effects on NF membrane performance. Two different NF membranes, from the same manufacturer, were tested in this study: one with high permeability and low salt removal capability (ESNA I), and the other with low permeability and high salt removal capability (ESNA II). The former membrane exhibited consistent NOM removal behaviour (greater than 75% based on DOC and stable permeabilities, when operated with pre-treatment of the MF membrane), while the latter membrane exhibited less stable performance in terms of NOM removal and permeability, even with chemical cleaning. Overall, the NF membrane exhibited very stable efficiencies of haloacetic acids formation potential and biodegradable dissolved organic carbon removals, in comparison with both CT processes and GAC.